The invention relates to marine propulsion systems, including marine transmission shifting systems.
In bass boat applications, when shifting from neutral to a forward or reverse gear, there is a drop in engine speed. This is due in large part to the load put on the engine by the high pitch propellers normally used in bass boat applications. The present invention addresses these and other types of boating applications where there is a drop in engine speed upon shifting into gear.
In the present invention, engine speed is increased in response to shifting into or out of gear. This is opposite to typical boating applications where engine speed is decreased, e.g. by interrupting the ignition, upon shifting into gear, in order to facilitate such shifting, for example Entringer U.S. Pat. No. 4,753,618 and Davis U.S. Pat. No. 4,726,798. Also known in the prior art are systems providing idle stabilization with spark timing along a negative slope such that as engine speed decreases, spark timing is advanced, and as engine speed increases, spark timing is retarded, thus providing self-stabilization, Staerzl U.S. Pat. No. 4,712,527. Such stabilization is a function of the ignition timing curve chosen for a particular speed range, not a shift condition.
In the present invention, to maintain an equal or nearly equal engine speed in-gear and out-of-gear, engine speed is changed upon shifting. In the preferred embodiment, ignition timing is advanced during the shift from neutral to forward and from neutral to reverse. When shifting back into neutral, the ignition timing is retarded, i.e. returned to its normal setting.
The altering of the ignition timing is performed electronically by connecting the ignition circuit through a resistor to ground. This is accomplished by mounting a switch on an existing shift plate. The shift plate is modified to provide mounting structure to accommodate the switch. An existing guide block on the shift plate is moved by the shift cable and is connected to the transmission for shifting the latter. The existing guide block is modified to have camming surfaces for actuating the switch between open and closed states to alter ignition timing.
In the preferred embodiment, when shifting into forward or reverse, the respective guide block camming surface becomes disengaged from the switch, such that the latter is in its normally closed state connecting the ignition circuit through the resistor to ground, which reduces the ignition circuit bias voltage and advances spark ignition timing electronically, which prevents the engine speed from dropping. Upon shifting back into neutral, the respective guide block camming surface engages the switch and actuates it to an open state, interrupting the noted connection through the resistor to ground, to return or retard ignition timing to its original point.